Abstract
Screening for severe combined immunodeficiency (SCID) was introduced into the Swedish newborn screening program in August 2019 and here we report the results of the first year. T cell receptor excision circles (TRECs), kappa-deleting element excision circles (KRECs), and actin beta (ACTB) levels were quantitated by multiplex qPCR from dried blood spots (DBS) of 115,786 newborns and children up to two years of age, as an approximation of the number of recently formed T and B cells and sample quality, respectively. Based on low TREC levels, 73 children were referred for clinical assessment which led to the diagnosis of T cell lymphopenia in 21 children. Of these, three were diagnosed with SCID. The screening performance for SCID as the outcome was sensitivity 100%, specificity 99.94%, positive predictive value (PPV) 4.11%, and negative predictive value (NPV) 100%. For the outcome T cell lymphopenia, PPV was 28.77%, and specificity was 99.95%. Based on the first year of screening, the incidence of SCID in the Swedish population was estimated to be 1:38,500 newborns.
Highlights
Severe combined immunodeficiency (SCID) describes a group of molecularly diverse diseases characterised by malfunction of the adaptive immune response due to the absence of T lymphocytes, B lymphocyte dysfunction or absence, and in certain conditions, the absence of natural killer cells [1]
All screening programs use PCR-based proprietary or commercially available methods to detect T cell receptor excision circles (TRECs) as a proxy for thymic output, with few programs referring children based on low KRECs
Children were referred for further examination based on low TRECs and or low KRECs [17,18]
Summary
According to the latest report of the International Union of Immunological Societies (IUIS, Berlin, Germany) defects in 18 genes are recognised to cause SCID [2]. Children affected by SCID appear healthy at birth in most cases but often present within the first six months of age with intractable diarrhoea, failure to thrive, pneumonia, and recurrent, treatment-resistant infections, frequently caused by opportunistic pathogens. Live vaccines such as rotavirus and BCG vaccines, which are included in many vaccination programs, can be life-threatening to a child with undiagnosed SCID. The condition is fatal and children with SCID usually die within the first two years of life [1,3,4,5]
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